It is well-known in the art of hot-dip coating of steel strip that uniform coatings can be achieved through the use of jet wipe nozzles, or air knives. It is also known that the shape of the gas discharge opening in such jet wipe nozzles affects the flow and thickness of the hot-dip coating from edge to edge across the width of the steel strip. Studies have shown that the velocity of the gas being expelled from such discharge opening will be uneven along the width of the opening if the opposed edges of the opening are parallel to each other. When the gas discharge opening has such a parallel gap profile, the hot-dip coating on the finished product tends to have a lighter coating at the center of the strip and a heavier coating at the edges of the strip. It is also well-known that when the shape of the gap profile is changed to a uniform slope from its center to a wider gap at its edge, the hot-dip coating will be more uniform in thickness across the width of the coated product.
Heretofore one method of changing the shape of the gap profile was through the use of a nozzle insert system as described in an article entitled "The Development of Air Coating Control for Continuous Strip Galvanizing", Pages 83-85 of the February, 1970 issue of Iron and Steel Engineer, and in U.S. Pat. No. 3,917,888 granted Nov. 4, 1975 to Beam. The insert system disclosed in the article and the Beam patent discloses using inserts which have been machined to a desired center to edge slope. To change the shape of the gap profile an insert, having the proper machined slope, is selected and is pushed into one side of the gas discharge opening while at the same time forcing a previously used insert out the opposite side of the opening. Such a system is effective in shaping the gap profile of the discharge opening but is limited by the number of different machined inserts available to an operator.
A second method of changing the shape of the gap profile is disclosed in U.S. Pat. No. 3,753,418 granted Aug. 21, 1973 to Roncan. Starting at line 38 in column 5, and as shown in FIG. 2 of the drawings, the lower lip 24 is provided with spaced pins 27 which can be drawn downward at selected distances, which can be different from pin to pin, so that the thickness of the fluid blade 6 may be adjusted as desired for its entire width, Roncan, however, neither discloses nor suggests a method for changing the shape of both opposed edges in a gas discharge opening.
And, finally, a third method of changing the shape of the gap profile of the gas discharge opening in a jet wipe nozzle is through the use of machined shims placed between the nozzle halves as disclosed in U.S. Pat. No 4,153,006 granted May 8, 1979 to Thornton, et al. In column 19, starting at line 61, and as shown in FIG. 10, Thornton discloses using tapered shims to regulate the gap profile of the gas discharge opening. Thornton neither teaches nor suggests a means for permitting further adjustment to the gap profile after the jet wipe nozzle is assembled.
Although the above patents and publication disclose effective solutions for changing the gap profile shape of a gas discharge opening in a jet wipe nozzle, they are either limited to a selected number of adjustments as dictated by the available machined inserts or shims, or provide adjustment for only one edge of the gas discharge opening.